Hydrogen Evolution Reaction Activities of Room-Temperature Self-Grown Glycerol-Assisted Nickel Chloride Nanostructures

Three-dimensional nanomaterials of desired structural/morphological properties and highly porous with a high specific surface area are important in a variety of applications. In this work, glycerol-mediated self-growth of 3-D dandelion flower-like nickel chloride (NiCl2) from nickel-foam (NiF) is obtained for the first time using a room-temperature (27 °C) processed wet chemical method for electrocatalysis application. Glycerol-mediated self-grown NiCl2 flowers demonstrate an excellent electrocatalytic performance towards the hydrogen evolution reaction (HER), which is much superior to the NiF (303 mV) and NiCl2 electrode prepared without glycerol (208 mV) in the same electrolyte solution. With a Tafel slope of 41 mV dec−1, the NiCl2 flower electrode confirms improved reaction kinetics as compared to the other two electrodes, i.e., NiF (106 mVdec−1) and NiCl2 obtained without glycerol (56 mV dec−1). The stability of the glycerol-based NiCl2 electrode has further been carried out for 2000 cycles with the overpotential diminution of just 8 mV, approving an electrocatalyst potential of glycerol-based NiCl2 electrode towards HER kinetics. This simple and easy growth process involves nucleation, aggregation, and crystal growth steps for producing NiCl2 nanostructures for electrocatalytic water splitting application through the HER process.

Tremella-like 2D Nickel-Copper Disulfide with Ultrahigh Capacity and Cyclic Retention for Hybrid Supercapacitors

Two-dimensional (2D) disulfides possess unique physical and chemical properties and are widely used in electronic and photoelectric devices. Tuning the composition and optimizing the structure of the disulfides are feasible approaches to designing target sulfides for hybrid supercapacitors. This work synthesizes the tremella-like nanosheet-connected (Cu_xNi_1-x)S₂ via solvothermal and sulfur-vapor vulcanization. The 2D (Cu_xNi_1-x)S₂ electrode performs a high reversible capacity (526.0 mA h g^-1 at 1 A g^-1), decent capacity retention (75.6%) at 10 A g^-1, and prolonged cyclic retention (94.4% over 15,000 cycles), which is higher than that of (Cu_xNi_1-x)O and monometallic sulfides of NiS₂ and CuS. The elevated electrochemical properties of (Cu_xNi_1-x)S₂ are attributed to the optimized composition with increased redox reaction, enlarged lattice distance, abundant active sites, and attractive electronic and ionic conductivity. Also, (Cu_xNi_1-x)S₂ and active carbon (AC) are assembled to form a hybrid supercapacitor (HSC). The (Cu_xNi_1-x)S₂//AC HSC demonstrates a maximum specific capacitance of 231.0 F g^-1 at 1 A g^-1 and a high energy density of 82.4 W h kg^-1 at a power density of 1.82 kW kg^-1. Outstanding cyclic retentions of 94.9 and 84.5% after 8000 and 10,000 cycles are also obtained. In conclusion, this result suggests a facile routine for preparing a novel 2D layer material of (Cu_xNi_1-x)S₂ with outstanding specific capacity and cycling performance for hybrid supercapacitors.

Facile In Situ Synthesis of Co(OH)2-Ni3S2 Nanowires on Ni Foam for Use in High-Energy-Density Supercapacitors

Ni3S2 nanowires were synthesized in situ using a one-pot hydrothermal reaction on Ni foam (NF) for use in supercapacitors as a positive electrode, and various contents (0.3-0.6 mmol) of Co(OH)2 shells were coated onto the surfaces of the Ni3S2 nanowire cores to improve the electrochemical properties. The Ni3S2 nanowires were uniformly formed on the smooth NF surface, and the Co(OH)2 shell was formed on the Ni3S2 nanowire surface. By direct NF participation as a reactant without adding any other Ni source, Ni3S2 was formed more closely to the NF surface, and the Co(OH)2 shell suppressed the loss of active material during charging-discharging, yielding excellent electrochemical properties. The Co(OH)2-Ni3S2/Ni electrode produced using 0.5 mmol Co(OH)2 (Co0.5-Ni3S2/Ni) exhibited a high specific capacitance of 1837 F g-1 (16.07 F cm-2) at a current density of 5 mA cm-2, and maintained a capacitance of 583 F g-1 (16.07 F cm-2) at a much higher current density of 50 mA cm-2. An asymmetric supercapacitor (ASC) with Co(OH)2-Ni3S2 and active carbon displayed a high-power density of 1036 kW kg-1 at an energy density of 43 W h kg-1 with good cycling stability, indicating its suitability for use in energy storage applications. Thus, the newly developed core-shell structure, Co(OH)2-Ni3S2, was shown to be efficient at improving the electrochemical performance.

Room-temperature chemical synthesis of 3-D dandelion-type nickel chloride (NiCl2@NiF) supercapattery nanostructured materials

A simple, room-temperature operable, glycerol-supported single beaker-inspired, and binder-free soft-chemical protocol has been developed to synthesize 3-D dandelion flower-type nickel chloride (NiCl₂) supercapattery (supercapacitor + battery) nanostructured electrode material from solid 3-D nickel-foam (NiF). The dandelion flower-type NiCl₂@NiF labeled as B electrode, demonstrates a battery-type electrochemical performance as obtained 1551 F·g^-1 specific capacitance (SC) and 95% cyclability over 50,000 cycles is higher than that of a setaria viridis-type NiCl₂@NiF electrode, prepared without glycerol labeled as A electrode. As a commercial market product, assembled NiCl₂@NiF@ (cathode)// BiMoO₃ (anode) pouch-type asymmetric supercapacitor energy storage device demonstrates moderate energy density and power density (28 Wh·kg^-1 and 845 W·kg^-1). By utilizing three devices in series, three different colored LEDs can be operated at full brightness. The as-proposed low temperature protocol impeccably effective and efficient on account of the low-cost, easy synthesis methodology for scalability, and high crytallinity as well as solvent-free and non-toxic as pyrolated gases were used while synthesis processing.

NiF2 Nanorod Arrays for Supercapattery Applications

A electrode for energy storage cells is possible directly on Ni foam, using a simple reduction process to form NiF2 nanorod arrays (NA). We demonstrate NiF2@Ni NA for a symmetric electrochemical supercapattery electrode. With an areal specific capacitance of 51 F cm-2 at 0.25 mA cm-2 current density and 94% cycling stability, a NiF2@Ni electrode can exhibit supercapattery behavior, a combination of supercapacitor and battery-like redox. The symmetric electrochemical supercapattery delivers 31 W h m-2 energy density and 797 W m-2 power density with 83% retention in a 1 M KOH electrolyte, constituting a step toward manufacturing a laboratory-scale energy storage device based on metal halides. Producing self-grown hierarchically porous nanostructured electrodes on three-dimensional metal foams by displacement reactions may be useful for other metal halides as electrodes for supercapacitors, supercapatteries, and lithium-ion batteries.

Electrocatalytic Water Splitting through the Ni x S y Self-Grown Superstructures Obtained via a Wet Chemical Sulfurization Process

We report water-splitting application of chemically stable self-grown nickel sulfide (Ni _x S _y ) electrocatalysts of different nanostructures including rods, flakes, buds, petals, etc., synthesized by a hydrothermal method on a three-dimensional Ni foam (NiF) in the presence of different sulfur-ion precursors, e.g., thioacetamide, sodium thiosulfate, thiourea, and sodium sulfide. The S^2- ions are produced after decomposition from respective sulfur precursors, which, in general, react with oxidized Ni²⁺ ions from the NiF at optimized temperatures and pressures, forming the Ni _x S _y superstructures. These Ni _x S _y electrocatalysts are initially screened for their structure, morphology, phase purity, porosity, and binding energy by means of various sophisticated instrumentation technologies. The as-obtained Ni _x S _y electrocatalyst from sodium thiosulfate endows an overpotential of 200 mV. The oxygen evolution overpotential results of Ni _x S _y electrocatalysts are comparable or superior to those reported previously for other self-grown Ni _x S _y superstructure morphologies.

Sulphur Source-Inspired Self-Grown 3D Ni xS y Nanostructures and Their Electrochemical Supercapacitors

Sulphur source-inspired self-grown polycrystalline and mesoporous nickel sulfide (Ni _xS _y) superstructures with vertically aligned nanomorphologies viz. rods, flakes, buds, and petals, synthesized at elevated temperatures and moderate pressures by a facile one-pot hydrothermal method on a three-dimensional Ni foam demonstrate remarkable areal specific capacitances of 7152, 4835, and 2160 F cm^-2 at current densities of 1, 2, and 5 mA cm^-2, respectively, with a cycling stability of 94% for a battery-type electrochemical supercapacitor when used as an electrode material in a supercapacitor. The Ni _xS _y//Bi₂O₃ asymmetric supercapacitor assembly exhibits an energy density of 41 W h·kg^-1 at a power density of 1399 W kg^-1 for 1 A g^-1 and was used in a three-cell series combination to operate a "GFHIM" display panel (our research institute name, Global Frontier R & D Center for Hybrid Interface Materials) composed of nearly 50 differently colored light-emitting diodes with high intensity in 1 M KOH water-alkali electrolyte. The electrochemical supercapacitor results obtained for the Ni _xS _y superstructures because of a combination of catalytically active amorphous and high mobility polycrystalline are highly comparable to those reported previously for salt-mediated and self-grown Ni _xS _y structures and morphologies.

A high-performance asymmetric supercapacitor based on Ni3S2-coated NiSe arrays as positive electrode

Cotton-like Ni₃S₂-coated NiSe rod composite electrode was synthesized by cyclic voltammetry electrodeposition with satisfactory electrochemical performance.

Fast ion transport through ultrathin shells of metal sulfide hollow nanocolloids used for high-performance energy storage

Metal sulfide (MS, nickel sulfide/copper sulfide) hollow spheres with hierarchical, ultrathin shell structures have been constructed by a facile method. The as-formed MS hollow structures are shown to be uniform in sizes with hierarchical ultrathin shells, which could facilitate the transport of electrolyte ions. Electrochemical evaluations of the as-fabricated MS based materials as supercapacitors electrodes having high large surface area (106–124 m² g⁻¹) and high specific capacitances (up to 1460 F g⁻¹) with good cycling stability (up to 94% retention after 5000 cycles), showing their potential applications in the next-generation high-performance supercapacitors used for energy storage.

Morphology controlled synthesis of 2-D Ni–Ni3S2 and Ni3S2 nanostructures on Ni foam towards oxygen evolution reaction

Catalysts for oxygen evolution reactions (OER) are at the heart of key renewable energy technologies, and development of non-precious metal catalysts with high activity and stability remain a great challenge in this field. Among various material candidates, metal sulfides are receiving increasing attention. While morphology-dependent catalytic performances are well established in noble metal-based catalysts, relatively little is known for the morphology‒catalytic performance relationship in metal sulfide catalysts. In this study, uniform spider web-like Ni nanosheets–Ni₃S₂ and honeycomb-like Ni₃S₂ structures are deposited on nickel foam (Ni₃S₂/NF) by a facile one-step hydrothermal synthetic route. When used as an oxygen evolution electrode, the spider web-like Ni–Ni₃S₂/NF with the large exposed surface area shown excellent catalytic activity and stability with an overpotential of ~310 mV to achieve at 10 mA/cm² and a Tafel slope of 63 mV/dec in alkaline media, which is superior to the honeycomb-like structure without Ni nanosheet. The low Tafel slope of the spider web-like Ni–Ni₃S₂/NF represents one of the best OER kinetics among nickel sulfide-based OER catalysts. The results point to the fact that performance of the metal sulfide electrocatalysts might be fine-tuned and optimized with morphological controls.

Ultra-tiny ZnMn2O4 nanoparticles encapsulated in sandwich-like carbon nanosheets for high-performance supercapacitors

Known as an excellent energy storage material, ZnMn₂O₄ has a wide range of applications in supercapacitors. In this report, a special sandwich-like structure of ZnMn₂O₄/C has been first designed and synthesized via a simple hydrothermal method and subsequent calcinations. The designed special sandwich-like structure can benefit ion exchange and remit the probable volume changes during a mass of electrochemical reactions. Furthermore, the porous carbon nanosheets, derived from low-cost glucose, can effectively increase ion flux. Therefore, the novel sandwich-like ZnMn₂O₄ nanoparticles encapsulated in carbon nanosheets can undoubtedly demonstrate an exceptional electrochemical performance for SCs. In this work, the composite material with porous sandwich-like structure exhibits excellent cyclic stability for 5000 cycles (∼5% loss) and high specific capacitance of 1786 F g^-1.

A super high performance asymmetric supercapacitor based on Co3S4/NiS nanoplates electrodes

In this paper, we successfully designed and synthesized Co₃S₄/NiS nanoplates by both ion-exchange action and Ostwald ripening reactions during the sulfurization process.

Vertically oriented Ni3S2/RGO/Ni3S2 nanosheets on Ni foam for superior supercapacitors

A unique sandwich structure of Ni₃S₂/RGO/Ni₃S₂ was designed on nickel foam by a one-step hydrothermal process.